Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$104.83	3.511%	$108.5106	$108.51	$108.50	$108.50
Purchase #2	$59.67	10.483%	$65.9252	$65.93	$65.95	$65.90
Purchase #3	$33.91	6.479%	$36.107	$36.11	$36.10	$36.10
Purchase #4	$100.67	8.570%	$109.2974	$109.30	$109.30	$109.30
Purchase #5	$39.85	12.110%	$44.6758	$44.68	$44.70	$44.70
Purchase #6	$152.78	10.263%	$168.4598	$168.46	$168.45	$168.50
Purchase #7	$23.62	12.635%	$26.6044	$26.60	$26.60	$26.60
7 purchase totals =	$515.33		$559.5802	$559.59	$559.60	$559.60